1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus. In particular, the invention relates to a photoelectric conversion apparatus provided with a function of adding a signal, and an image pickup system.
2. Description of the Related Art
A photoelectric conversion apparatus is used in photoelectric conversion apparatus such as a digital still camera or a digital camcorder. Various requests are made for the photoelectric conversion apparatus. One of the requests is an improvement in an output rate. To realize a high output rate, a technology is suggested in which signals based on plural pixels in the photoelectric conversion apparatus are added to each other to reduce the number of signals output from the photoelectric conversion apparatus. By adding the signals to each other, it is possible to obtain the high output rate while a decrease in an image quality caused by a decrease in a resolution is suppressed.
Japanese Patent Laid-Open No. 2010-68123 discloses an image pickup apparatus configured to add signals in a direction along a row and a direction along a column with respect to pixels arranged in a matrix manner. Japanese Patent Laid-Open No. 2010-68123 discloses a weighting addition conducted in a horizontal direction, that is, the direction along the row.
However, according to the configuration disclosed in Japanese Patent Laid-Open No. 2010-68123, the number of connected switches varies between two holding capacitors provided to the respective columns of the pixels, and a difference may be generated in capacitance values between the two holding capacitors. As a result, charge quantities held in the respective holding capacitors may be different from each other, and an image quality of a generated image may be degraded.